Integrated Sequence Physics Chemistry Organic Biology
 Work, Energy, and PowerWorkKinetic EnergyPotential EnergyPotential Energy of Objects Near the Earth's SurfacePotential Energy of the Mass-SpringPotential Energy of Gravitational and Electrodynamic SystemsConservation of energyLaw of conservation of energyConservative versus non-conservative forcesEnergy lossSimple MachinesPower

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 Special points of emphasis
 Work, Energy, and PowerGravitation As we discussed earlier within Newton's Laws, there are two main types of gravity problems, those in which the gravitational force is virtually constant over the distances involved and those in which the gravitational force changes with varying position within the system.Each of these different models has a different approach to energy. The manner of describing changes in energy is different in a constant force system versus a system where force changes with position.In both cases, however, as work is done against or by the field, as the object is changing position, its state of potential energy is changing. As two attracting objects are moved further apart, the potential energy of the system increases whether an object is being raised from the surface of the Earth or whether two objects are separating in outer space.On the surface of the Earth, where the distances over which the object is going to move will be relatively small, it is more convenient to assign zero as the potential energy on the ground.For situations in outer space, however, where the force can be seen to decrease the further apart the objects are moved, zero potential energy represents the state of the objects when they are infinitely far apart. All other values are negative. Think about this. Make sure you understand this.In both cases, potential energy increases with increasing separation, and if you applied the outer space model to the object near the Earth's surface, you would compute the same change in energy. The outer space model is the more descriptive of reality, because it shows gravitational potential energy as a form of binding energy. Two objects under the influence of mutual gravitation have fallen into a potential energy well together. They have fallen together into the well of their mutual binding energy. The magnitude of negative potential energy shows how much energy would have to be imparted to the system to allow the objects to escape from each other.
 Work, Energy, and PowerElectricity As we discuss the fundamental principles of Work, Power & Energy, keep in mind that electrostatic systems will be a primary field of application for these concepts. When a positive charge is moved towards another positive charge, potential energy increases. Energy is being stored in the system. However, when a negative charge is moved towards a positive charge, potential energy decreases and the system is losing potential energy.The behavior of oppositely charged particles, distinguished by a force of mutual attraction, is similar to gravitational force. The energy description of oppositely charged particles is analogous to the behavior of two masses interacting through gravitational force. The nearer the objects, the lower the potential energy with both gravitational force between masses and the electric force between unlike charges.